1. Field of the Invention
The invention relates to a process for the preparation of organopolysiloxanes having aminoalkyl groups.
2. Background Art
Organopolysiloxanes carrying aminoalkyl groups, referred to below as amine oils, are among the most important organically functionalized organopolysiloxanes and are successfully used in many different applications. These include, inter alia, textile finishing, building protection, cosmetic formulations or the treatment of surfaces. In most applications in these areas, it is important to use amine oils which have a high quality. The corresponding quality features include a) a residual volatility which is constant and as low as possible (e.g. due to short-chain alcohols, short-chain and/or cyclic siloxane components or amines), b) a constant viscosity, c) an optimum random distribution of the aminoalkyl groups in the copolymer and, where possible and necessary, d) optical clarity (freedom from turbidity). Especially the quality features b) and c) can generally be achieved only by effective equilibration of the polymer mixture, if appropriate coupled to a condensation reaction, although different amounts of volatile compounds are obtained depending on the reaction conditions set.
Amine oils are generally prepared by condensation and/or equilibration reactions between linear or cyclic organopolysiloxanes and aminoalkyl-functionalized alkoxysilanes or the partial or complete hydrolysis products thereof, generally under the action of catalytic amounts of basic inorganic or organic compounds.
According to the prior art at present, amine oils are prepared in a so-called batch process, i.e. campaign-by-campaign in batchwise processes in stirrers. Stirrers are very flexible owing to the variety of chemical reactions which can be carried out in them but—compared with continuous processes—are uneconomical in the case of very large production campaigns and high mass throughputs. This is due in particular to the fact that they can be automated only to a certain degree and that it is necessary to accept long times for heating up and cooling down, and for filling and emptying containers having a capacity of several cubic meters, thus entailing high operating costs and high labor costs. In addition, it is necessary to accept holding times of the reaction product, during which, for example, quality testing of the product is carried out. In particular, however, there are inevitably variations in the product composition and product quality from different production campaigns, with the result that product specifications have to be more widely formulated and high qualities are more difficult to achieve. Not least, a stirrer occupies substantially more space compared with a continuously operated plant and its throughput can be increased only through very great technical complexity or not at all (upscaling, debottlenecking).
One difficulty of current amine oil syntheses is the deactivation of the condensation or equilibration catalyst. If the basic catalyst is neutralized in a conventional manner with an acid, as described, for example, in U.S. Pat. No. 5,077,421, turbidity occurs as result of salt precipitates. However, continuous or semicontinuous filtration of a continuously produced amine oil is not desired since this gives rise to technical difficulties (e.g. change of filter in continuous operation), and the space-time yield decreases.
One possibility for avoiding such turbidity is the method of deactivating the tetraalkylammonium hydroxides or ammonium phosphates and borates used by thermal decomposition after the end of the reaction, as described, for example, in U.S. Pat. No. 4,652,662 (corresponding DE A 3418358). The resulting decomposition products must, however, be removed by distillation in vacuo. It is known to those skilled in the art that vacuum distillation takes several hours, is also energy-consumptive, and owing to the necessary residence time, cannot readily be carried out continuously. Finally, owing to traces of volatile organic amines, the process generally leads to an annoying and unacceptable odor during the use of the amine oils thusly prepared.
U.S. Pat. No. 7,129,369 (corresponding EP-A 1580215) describes a process in which, in spite of the use of alkali metal hydroxides and alcoholates, turbidity-free amine oils are obtained without a filtration step by neutralization with silyl phosphates, with the result that silicone-soluble neutralization products are obtained.
U.S. Pat. No. 4,128,568 (corresponding DE-A 2705563) describes a continuous process for the preparation of unfunctionalized organopolysiloxanes. The alkali metal hydroxides used must be deactivated by addition of trimethylchlorosilane. The organopolysiloxanes thus obtained must therefore be subjected to a downstream filtration and distillation step in order to remove the volatile disiloxanes produced by deactivation and thus to achieve the desired low residual volatility.
EP-A 1723193 describes a catalyst-free continuous process for the preparation of siloxanes having terminal aminoalkyl functions from siloxanes carrying terminal SiOH groups and cyclic silazanes. However, with cyclic silazanes, the process starts from a special and complicated amine precursor, inter alia with the aim of keeping the amine oil obtained free of volatile alcohols resulting from condensation reactions. In addition, siloxanes which carry on-chain SiOH groups which are required to produce amine oils having side groups by this process are not easily and directly accessible.
Continuous processes, as described, for example, in U.S. Pat. No. 3,853,934, in which the organopolysiloxane building blocks to be condensed are passed over an acidic silicate fixed-bed catalyst are not suitable for the preparation of amine oils since the amine groups spontaneously form salts with the acid groups and would deactivate the catalyst.
EP-A 0982347 describes a continuous process for the preparation of silicone polymers from siloxanes carrying SiOH groups or cyclic siloxane by means of catalytic amounts of basic phosphazenes. Apart from terminal group functionalization with various SiC-bonded hydrocarbon radicals, however, no heteroatom-substituted organically functionalized copolymers, such as, for example, amine oils, are described.
A very special continuous reactor for the preparation of siloxane polymers from siloxane mono- and oligomers is described in EP-A 0522776. There, the reaction mixture is foamed and passes through a porous wall into the reaction space. As a result of the large interface produced between the reaction mixture and gas space, volatiles can be readily removed from low-viscosity media. However, the process described is limited to condensation reactions of monomers or low-viscosity oligomers, and express equilibration of the polymers produced or the preparation of highly viscous silicone oils is not described. Moreover, a conventional neutralization of the catalysts is described, which generally leads to turbid products owing to salt formation.
Common to all processes described above is that the amine oils produced thereby cannot simultaneously exhibit satisfactory, and in particular, constant properties with respect to the principal quality features of residual volatility, quality of equilibration and, if appropriate, freedom from turbidity and constancy thereof. Downstream filtration or devolatilization steps or subsequent processing by equilibration would be necessary.